Why are there so many options for vehicular gasoline at the pumps and what’s even the difference between them?
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Different engines are designed for gas that have slightly different properties. The property is called “octane.” Technically, it has to do with the engine compression ratio. There is not magic or value to higher octane gas for your car if it is not designed for it. Even cars driving in the last 10 years++ that are DESIGNED for specific octane fuel don’t care because their computers compensate for the 87 octane instead of their called out 91 octane.
In internal combustion engines, there is a thing called ‘compression ratio’. The higher this number is, the more squeeze applied to the fuel air mixture during the compression step before the combustion step. This compression heats up the fuel air mixture and can cause it to combust prematurely. The higher the octane rating, the more the fuel air mixture can be compressed before combusting. If you use gas with too low of an octane rating, it will combust before it is supposed to which can, at best, cause some knocking, or at worst, actually damage your engine and break it. Use whatever octane rating your car specifies. Definitely no lower, but also no higher because then you’re just wasting your money.
The octane rating determines what temp the gas in the car is prone to combust when put under compression. The higher the octane, the higher the resistance to combusting early in the cylinder during the compression stroke.
So, one option is diesel, which is not gasoline. Diesel engines work fundamentally differently than a gas engine, it’s a whole thing. You might also see E85, which is similarly for engines specifically designed for it.
The gas options, 91, 93, etc, refer to a thing called octane rating.
TL;DR is in 99% of cases it doesn’t really matter, just use what’s recommended in the manual. Cars are *generally* designed to work within a range of octane ratings and as long as you’re using the recommended octane or higher, everything will be fine. Going below that value can cause issues though.
The higher the octane rating, the more the gas resists combustion (it’s harder to make explode)
In a performance or high end engine, they use higher octane gas to avoid having the combustion cycle happen when and/or where it isn’t supposed to, which is bad for your engine.
This is more applicable in high end engines *typically but not exclusively* because of more aggressive timing and/or higher RPM and/or forced induction. Basically, in any circumstance where more precision is required because things are happening really quickly or in a really strong fashion.
Higher octane fuels don’t really do anything other than that, and most cars nowadays have an octane sensor and will self correct depending on the gas you use.
If your car has an octane sensor it *can* make slightly less power on lower octane fuel, but the difference may be close to nothing or a fair bit depending on the car/person/application. To be clear, your not making more power from higher octane, the engine is just making less power to prevent issues from lower octane fuel.
It doesn’t help clean anything or reduce buildup or whatever though, if you care about that you need to care about where you get your gas from over octane rating. Getting gas from someone like Shell is going to be cleaner than gas from your local whoever yaknow?
Also, fun fact, at many gas stations there is no such thing as mid grade fuel. It varies, but many gas stations just mix low and high grade to create mid grade at the pump, over having an independent tank. It depends though, some have an independent mid grade tank.
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